Near infrared (NIR) fluorescence has potential importance in the medical field, particularly in diagnostics and image-guided surgery. However, the availability of suitable fluorophores as imaging agents has been a primary hindrance. To be clinically viable, the ideal NIR fluorophore should have both good optical properties and superior in vivo properties with respect to solubility, biodistribution, and clearance. Most current fluorophores contemplated for use as imaging agents fail in connection with their in vivo properties. For example, known fluorophores tend to clear through the liver, which results in undesirable fluorescence throughout the gastrointestinal tract. And in some cases, known fluorophores suffer from significant non-specific background uptake in normal tissues, resulting in a low signal-to-background ratio. Accordingly, there is a current need for new and improved NIR fluorescent imaging agents, particularly those that can equilibrate rapidly between the intravascular and extravascular spaces and are cleared efficiently by renal filtration. The imaging agents of the invention are directed toward these and other needs.